铁矿石的还原性
参考答案：
指铁矿石被还原性气体CO或H2还原的难易程度。
研究表明，H1N1流感球形病毒细胞的直径约为0.00000156m，用科学记数法表示这个数为______．
Mary went to the box office at lunch time, but all the tickets ____out.
A．would sell
B．had sold
C．have sold
D．was selling
